Glass base material elongating method and glass base material elongating apparatus

ABSTRACT

A glass base material elongating method of sequentially feeding rod-like glass base materials hung by a glass base material feeding mechanism into a heating furnace, and pulling a glass rod with a smaller diameter by a pulling chuck at a lower part of the heating furnace, includes: aligning, by an alignment guiding device that guides the glass rod, a guiding center of the alignment guiding device with an axis of the glass rod, the alignment guiding device guiding the glass rod between the heating furnace and the pulling chuck.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 13/869,987, filed on Apr. 25, 2013, which claims priority toJapanese Patent Application No. 2012-105127, filed on May 2, 2012, thecontents of each of which are incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a glass base material elongating methodand a glass base material elongating apparatus.

2. Related Art

An example of glass base materials is an optical fiber preform that isformed with a quartz glass rod. In one method of manufacturing a glassbase material, a glass base material with a large diameter ismanufactured in advance, and then the glass base material is heated andelongated to manufacture a glass rod with a smaller diameter than thatof the glass base material. The glass base material with the largediameter is hung to be vertically long in an elongating furnace, and inthis state, a pulling dummy attached to a lower part of the glass basematerial is pulled down to elongate the glass base material.

SUMMARY

At the step of elongation in an elongating furnace, a glass rod may bebent due to the weight of a glass base material, and this may degradethe yield or productivity.

A first aspect of the present invention provides a glass base materialelongating method of sequentially feeding rod-like glass base materialshung by a glass base material feeding mechanism into a heating furnace,and pulling a glass rod with a smaller diameter by a pulling chuck at alower part of the heating furnace, the method including: aligning, by analignment guiding device that guides the glass rod, a guiding center ofthe alignment guiding device with an axis of the glass rod, thealignment guiding device aligning between the heating furnace and thepulling chuck.

A second aspect of the present invention provides a glass base materialelongating apparatus that extends a rod-like glass base material, andmanufactures a glass rod with a smaller diameter, the apparatusincluding: a heating furnace; a glass base material feeding mechanism;and a glass rod pulling chuck, wherein the glass base materialelongating apparatus further comprises an alignment guiding device thataligns, between the pulling chuck and the heating furnace, a guidingcenter of the alignment guiding device with an axis of the glass rod.

The summary clause does not necessarily describe all necessary featuresof the embodiments of the present invention. The present invention mayalso be a sub-combination of the features described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a structure of an elongatingapparatus 100.

FIG. 2 is a schematic plan view of an alignment guiding device 14.

FIG. 3 is a schematic plan view of the alignment guiding device 14.

FIG. 4 is a schematic diagram of the alignment guiding device 14.

FIG. 5 is a schematic diagram of the alignment guiding device 14.

FIG. 6 is a schematic diagram of the alignment guiding device 14.

FIG. 7 is a schematic diagram of the alignment guiding device 14.

FIG. 8 is a graph that illustrates changes in loads that are applied toa pulling mechanism 3.

FIG. 9 is a diagram for explaining the degree of bending (BOW values) ofa glass rod 10.

FIG. 10 is a schematic diagram of an alignment guiding device 25.

FIG. 11 is a schematic diagram of an alignment guiding device 25.

FIG. 12 is a schematic diagram of an alignment guiding device 25.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, (some) embodiment(s) of the present invention will bedescribed. The embodiment(s) do(es) not limit the invention according tothe claims, and all the combinations of the features described in theembodiment(s) are not necessarily essential to means provided by aspectsof the invention.

First Embodiment

FIG. 1 is a schematic diagram showing a structure of a glass basematerial elongating apparatus 100. The elongating apparatus 100 includesa feeding mechanism 2, a heating furnace 1, an alignment guiding device14 and a pulling mechanism 3, all of which are provided in this orderfrom above in the direction of the gravitational force.

A glass base material 5 is hung via a hanging connecting part 4 in thefeeding mechanism 2. A lower part of the glass base material 5 isconnected to the pulling mechanism 3 via a pulling dummy 6 and a pullingchuck 7. The pulling chuck 7 has a load meter that measures loads thatare applied vertically upward and downward.

The heating furnace 1 has, for example, a carbon heater. For the purposeof preventing wear due to oxidation, inert gas such as nitrogen andargon is introduced into the heating furnace 1. Also, for the purpose ofpreventing the outside air from entering into the heating furnace 1, atop chamber 8 and a furnace exit gas seal 9 are provided.

The glass base materials 5 are sequentially fed into the heating furnace1 by the feeding mechanism 2, and heated and softened by the heatingfurnace 1. A lower part of the glass base material 5 is pulled by thepulling mechanism 3, and thereby a glass rod 10 with a smaller diameteris formed. Accordingly, a lowering rate V2 of the pulling mechanism 3 isset to be faster than a lowering rate V1 of the feeding mechanism 2. Thelowering rates V1, V2 are adjusted so that an outer diameter of theglass rod 10 is kept constant.

Furthermore, the alignment guiding device 14 is provided between thepulling chuck 7 and the heating furnace 1. The alignment guiding device14 guides the glass rod 10 in a state that a guiding center of thealignment guiding device 14 is aligned with an axis of the elongatedglass rod 10.

FIG. 2 is a schematic plan view showing only the alignment guidingdevice 14, and mainly shows an aligning mechanism of the alignmentguiding device 14. Also, FIG. 2 shows a state that the alignment guidingdevice 14 is not guiding the glass rod 10.

The alignment guiding device 14 has a base plate 15 and a plurality ofguiding rollers 17. The base plate 15 has a through-hole at a centerthereof through which the glass rod 10 is inserted.

Each of the plurality of guiding rollers 17 is mounted individually on aslide table 16 that is driven by an air cylinder provided on the baseplate 15. The guiding rollers 17 are formed, for example, with carbon.

The slide tables 16 are connected by three synchronized wires 19 via sixguiding pulleys 18 attached to the base plates 15. Thereby, the threeslide tables 16 are driven in synchronization with each other.Accordingly, regardless of the positions of the slide tables 16, thecenter of the three guiding rollers 17, i.e., the guiding center of thealignment guiding device 14, is kept at one position.

FIG. 3 is a schematic plan view of the alignment guiding device 14, andshows a state that the alignment guiding device 14 is guiding the glassrod 10. As described above already, the three slide tables 16 are drivensynchronously, and the guiding center of the alignment guiding device 14is always kept at one position. Accordingly, when all the three guidingrollers 17 abut on the glass rod 10, the axis of the glass rod 10matches with the guiding center of the alignment guiding device 14.

FIG. 4 is a schematic side view showing an initial state of operation ofthe alignment guiding device 14. For simplifying explanation, thealignment guiding device 14 is illustrated schematically in FIG. 4 byproviding a pair of the guiding rollers 17 on the same plane.

The alignment guiding device 14 has a plurality of gas blow/suctionblocks 21 supported by mounts 20. The plurality of gas blow/suctionblocks 21 supports the base plates 15. Also, the gas blow/suction blocks21 have gas outlet/inlet ports 22. When compressed gas is supplied tothe gas outlet/inlet ports 22, the gas blow/suction blocks 21 blow gasfrom the upper surfaces in the figure to float the base plate 15.Thereby, the base plate 15 can slide in the horizontal direction easilyand smoothly with a small force.

As described above already, the plurality of slide tables 16 and theplurality of guiding rollers 17 are provided on the base plates 15, andthese collectively form an aligning mechanism. In the aligningmechanism, the plurality of guiding rollers 17 are driven insynchronization with each other.

FIG. 5 shows the following state in the operation of the alignmentguiding device 14. When the slide tables 16 are driven synchronously ina state that the base plates 15 are floated as stated above, any one ofthe guiding roller 27 first abuts on the glass rod 10. Furthermore, bycontinuing driving the slide tables 16 synchronously, the base plates 15slide and move on the gas blow/suction blocks 21.

FIG. 6 shows the following state in the operation of the alignmentguiding device 14. By further continuing driving the slide tables 16 asstated above, all the guiding rollers 17, 27 eventually abut on theglass rod 10, and the slide tables 16 and the base plates 15 stop.

When the base plate 15 is floating over the gas blow/suction block 21,the position of the glass rod 10 changes little in the above-describedoperation because the force of the guiding roller 27 that presses theglass rod 10 is very small. Accordingly, the guiding center of thealignment guiding device 14 is aligned toward the axis of the guidingrod 10 in the course of reaching the state shown in FIG. 6.

FIG. 7 shows the following state in the operation of the alignmentguiding device 14. When the alignment guiding device 14 is aligned asdescribed above, gas is discharged from the gas outlet/inlet port 22,and the gas blow/suction block 21 is evacuated to be in a vacuum state.Thereby, the gas blow/suction block 21 vacuum-suctions the base plate15, and fixes the horizontal position of the base plate 15. Thereby, thestate that the alignment guiding device 14 is aligned with the axis ofthe glass rod 10 is maintained.

In this manner, the alignment guiding device 14 can align with the glassrod 10 without changing the position of the glass rod 10 by closing theguiding rollers 17 toward the axis of the glass rod 10 in the aligningmechanism. Also, the alignment guiding device 14 can be kept aligned bythe fixing mechanism.

FIG. 8 is a graph that illustrates changes over time in loads that areapplied vertically to the pulling mechanism 3 in the elongatingapparatus 100. In FIG. 8, the positive side of the vertical axis shows aforce that is applied vertically downward, and the negative side shows aforce that is applied vertically upward.

When the temperature of the heating furnace 1 in the elongatingapparatus 100 is relatively high, the viscosity of a neck-down 11 of theglass base material 5 becomes lower, and the weight of the glass rod 10is applied vertically downward to the pulling mechanism 3. Thereby, adownward force is applied to the pulling mechanism 3.

On the contrary, when the temperature of the heating furnace 1 in theelongating apparatus 100 is relatively low, the viscosity of theneck-down 11 is high; as a result, a large force is required to deformthe glass base material 5 and pull the glass rod 10. Accordingly, avertically upward force, i.e. a force to pull up the pulling mechanism3, is applied to the pulling mechanism 3.

Furthermore, as the elongation proceeds and the weight of the glass rod10 increases, a force that is applied vertically downward to the pullingmechanism 3 becomes gradually larger even when the temperature of theheating furnace does not change. In addition, when the outer diameter ofthe glass base material 5 fluctuates, the force that is applied to thepulling mechanism 3 fluctuates also.

In the illustrated curve, although a waveform 12 is observed due to adiametrical fluctuation of the glass base material 5 in a period 12 inthe beginning of elongation, the load shows an overall increase.Accordingly, the load indicated by the curve shifts from the negativeside to the positive side. It can be estimated based on this that in thebeginning of elongation, the pulling mechanism 3 pulls down, elongatesand deforms the glass rod 10, but, in the last half of elongation, thepulling mechanism 3 receives a fall of the glass rod 10 due to itsweight to control the rate of the fall.

Furthermore, in a period 13 immediately before the end of elongation, anoticeable increase of the load applied to the pulling mechanism 3 isobserved. It can be estimated that this phenomenon is caused due toheating and accordingly softening of a tapered portion that ispositioned at an upper portion of the glass base material 5 and isthinner than a straight barrel portion.

In an area A, in the illustrated graph, where a load is applied upwardto the pulling mechanism 3, bending of the glass rod 10 is unlikely tooccur because a tensile force is applied to the glass rod 10. On theother hand, in an area B where a load is applied downward to the pullingmechanism 3, a force that may cause the glass rod 10 to fall down aboutthe pulling chuck 7 may be applied to the glass rod 10 because thepulling mechanism 3 is supporting the glass rod 10 to prevent it fromfalling down due to its weight.

When a force that may cause the glass rod 10 to fall down is applied tothe glass rod 10, bending of the glass rod 10 may be generated due toaxial deviation between the axis of the glass rod 10 and the axis of theglass base material 5 at the neck-down 11. When bending has occurred tothe glass rod 10, the bent portion of the glass rod 10 has to bediscarded or repaired, and this leads to degradation of themanufacturing cost and yield of the glass rod 10.

In the elongating apparatus 100, changes in the loads that are appliedto the pulling mechanism 3 can be detected by the load meter provided tothe pulling chuck 7. In such operation, the alignment guiding device 14is activated immediately before or immediately after a downward loadstarts to be applied to the pulling mechanism 3. Thereby, the guidingcenter of the alignment guiding device 14 can be aligned with the axisof the glass rod 10 by moving, and at the same time aligning, theguiding rollers 17 with the axis of the glass rod 10.

Also, the state that the alignment guiding device 14 is aligned ismaintained by fixing the aligning position by fixing the guiding rollers17 with the fixing mechanism. Accordingly, the alignment guiding device14 guides the glass rod 10 while the guiding center is kept matchingwith the axis of the glass rod 10.

Thereby, deviation of the axis of the glass rod 10 from the axis of theglass base material 5 is suppressed, and bending of the glass rod 10 canbe prevented from occurring. Accordingly, because elongation can becontinued without the glass rod 10 falling down, the glass rod 10 withfew bends can be manufactured stably.

The center position of the glass rod 10 differs for each glass basematerial 5 to be elongated. Accordingly, bending of the glass rod 10 canbe prevented for each glass base material 5 by performing alignment bythe alignment guiding device 14 for each glass base material 5 to beelongated.

Also, the three guiding rollers 17 are provided to the alignment guidingdevice 14 in the above-described elongating apparatus 100. However, thenumber of the guiding rollers 17 is of course not limited to three, butmay be larger, and the glass rod 10 may be guided by using a part or allof the guiding rollers 17.

Example 2

FIG. 10 shows an initial state of operation of another alignment guidingdevice 25. FIG. 10 is illustrated as seen from the same perspective asthat of FIG. 4, the same elements as those in FIG. 4 are provided withthe same reference numerals, and explanation is not repeated.

The alignment guiding device 25 is provided with a horizontal positionadjusting mechanism 23 and a rod position identifying device 24. Thehorizontal position adjusting mechanism 23 is mounted on a mount 20. Abase plate 15 is mounted on the horizontal position adjusting mechanism23. A slide table 16 and a carbon guiding roller 17 are attached on thebase plate 15. The horizontal position adjusting mechanism 23 may be,for example, an electrically-driven XY table.

The rod position identifying device 24 is fixed on the mount 20, andmeasures the horizontal position of a glass rod 10. That is, the rodposition identifying device 24 consists of two pair of devices that canmeasure the horizontal position of the glass rod 10, one pair beingdedicated to measure the position in the X direction, and the other pairbeing dedicated to measure the position in the orthogonally-crossing Ydirection. Each of the rod position identifying device 24 may be any oneof a combination of a camera and an image processing device, a laserdiameter measurement instrument and a laser ranging instrument.

In the state shown in FIG. 10, all of the guiding rollers 17 areseparated from the glass rod 10, and the glass rod 10 is not guided bythe alignment guiding device 25. In this state, the rod positionidentifying device 24 measures the position of the glass rod 10.

FIG. 11 shows the following state in the operation of the alignmentguiding device 25. The horizontal position adjusting mechanism 23 movesthe base plate 15 based on the positional information of the glass rod10 identified by the rod position identifying device 24, and matches thecenter of the plurality of guiding rollers 17 with the axis of the glassrod 10. In this step, the horizontal position adjusting mechanism 23fixes the position of the base plate 15.

FIG. 12 shows the following state in the operation of the alignmentguiding device 25. The slide tables 16 move synchronously in thealignment guiding device 25, and each of the guiding rollers 17 abuts onthe glass rod 10. Thereby, the alignment guiding device 25 guides theglass rod 10 while the axis of the glass rod 10 is kept matching withthe guiding center of the alignment guiding device 14.

In this manner, the guiding center of the alignment guiding device 25having a different structure can also be matched with the axis of theglass rod 10. Thereby, deviation of the axis of the glass rod 10 fromthe axis of the glass base material 5 is suppressed, and bending of theglass rod 10 can be prevented from occurring.

Experiment Example 1

A glass base material 5 with the length of a straight barrel part ofapproximately 2000 mm and the outer diameter of approximately 180 mm waselongated to form a glass rod 10 with the length of approximately 2530mm and the outer diameter of 160 mm, by using the elongating apparatus100 provided with the alignment guiding device 14. When a downward loadstarted to be applied to the pulling mechanism in the last half ofelongation, the slide tables 16 were operated synchronously, the guidingcenter of the alignment guiding device 14 was aligned with the axis ofthe glass rod 10, and the aligning mechanism was fixed at this position.

The degree of bending (BOW values) of the twenty thus-elongated glassrods 10 was measured, and the result showed the average value of 0.55mm/m, and the maximum value of 1.02 mm/m. FIG. 9 shows a BOW valuemeasurement method that was used. BOW values are obtained by dividingmaximum widths G [mm] of whirling that occurred when the glass rods weresupported and rotated by rollers that were positioned 50 mm away fromboth the ends of the glass rods, by the interval L [mm] between therollers.

Experiment Example 2

A glass base material 5 with the length of a straight barrel part ofapproximately 2000 mm and the outer diameter of approximately 180 mm waselongated to form a glass rod 10 with the length of approximately 2530mm and the outer diameter of 160 mm, by using the elongating apparatus100 provided with the alignment guiding device 25. When a downward loadstarted to be applied to the pulling mechanism in the last half ofelongation, the slide tables 16 were operated synchronously, the guidingcenter of the alignment guiding device 14 was aligned with the axis ofthe glass rod 10, and the aligning mechanism was fixed at this position.The degree of bending (BOW values) of the twenty thus-elongated glassrods 10 was measured, and the result showed the average value of 0.59mm/m, and the maximum value of 0.98 mm/m.

Comparative Example 1

A glass base material 5 was elongated by using the elongating apparatus100 provided with the alignment guiding device 14, but without guidingby the alignment guiding device 14. The glass base material 5 with thelength of a straight barrel part of approximately 2000 mm and the outerdiameter of approximately 180 mm was elongated to form a glass rod 10with the length of approximately 2530 mm and the outer diameter of 160mm. Elongation was continued without activating the alignment guidingdevice 14 even when a downward load started to be applied to the pullingmechanism in the last half of elongation. The degree of bending (BOWvalues) of the twenty thus-elongated glass rods 10 was measured, and theresult showed the average value of 1.58 mm/m, and the maximum value of3.26 mm/m; thus, the degree of bending that was higher than those inExperiment Examples 1 and 2 was observed.

As can be seen, the elongating apparatus 100 elongates the glass rod 10while guiding the glass rod 10 by using the alignment guiding device 14.Thereby, the glass rods 10 with few bends can be manufactured stably.

While the embodiment(s) of the present invention has (have) beendescribed, the technical scope of the invention is not limited to theabove described embodiment(s). It is apparent to persons skilled in theart that various alterations and improvements can be added to theabove-described embodiment(s). It is also apparent from the scope of theclaims that the embodiments added with such alterations or improvementscan be included in the technical scope of the invention.

The operations, procedures, steps, and stages of each process performedby an apparatus, system, program, and method shown in the claims,embodiments, or diagrams can be performed in any order as long as theorder is not indicated by “prior to,” “before,” or the like and as longas the output from a previous process is not used in a later process.Even if the process flow is described using phrases such as “first” or“next” in the claims, embodiments, or diagrams, it does not necessarilymean that the process must be performed in this order.

What is claimed is:
 1. A glass base material elongating apparatus thatextends a rod-like glass base material, and manufactures a glass rodwith a smaller diameter, the apparatus comprising: a heating furnaceinto which a glass base material is fed; a glass base material feedingmechanism that hangs the glass base material to be fed into the heatingfurnace; a glass rod pulling chuck that pulls a glass rod at a lowerpart of the heating furnace, the pulling of the glass rod establishingan axis of the glass rod; and an alignment guiding device whose guidingcenter can be shifted such that the guiding center conforms to theestablished axis of the glass rod, the alignment guiding device guidingthe glass rod between the heating furnace and the pulling chuck, whereinthe alignment guiding device includes an aligning mechanism that alignsthe guiding center of the alignment guiding device with the establishedaxis of the glass rod under a force that is insufficient to move theglass base material in a manner that substantially changes theestablished axis of the glass rod.
 2. The glass base material elongatingapparatus according to claim 1, wherein the alignment guiding devicehas: a fixing mechanism that fixes the aligning mechanism at a positionwhere the guiding center of the alignment guiding device is aligned withthe established axis of the glass rod.
 3. The glass base materialelongating apparatus according to claim 2, wherein the aligningmechanism includes a plurality of guiding rollers that abut on and arespaced apart from the glass rod, and the plurality of guiding rollersmoves synchronously.
 4. The glass base material elongating apparatusaccording to claim 2, further comprising a load meter that measures aload that is applied vertically to the pulling chuck.
 5. The glass basematerial elongating apparatus according to claim 2, wherein thealignment guiding device has: a floating mechanism that floats thealigning mechanism; and a fixing mechanism that fixes the aligningmechanism by vacuum-sucking.
 6. The glass base material elongatingapparatus according to claim 1, wherein the alignment guiding device hasa horizontal position adjusting mechanism that adjusts a horizontalposition of the glass rod, and a rod position identifying device thatidentifies a position of the glass rod.
 7. The glass base materialelongating apparatus according to claim 6, wherein the horizontalposition adjusting mechanism includes an electrically-driven XY table.8. The glass base material elongating apparatus according to claim 6,wherein the rod position identifying device includes any one of acombination of a camera and an image processing device, a laser diametermeasurement instrument, and a laser ranging instrument.